1. Field of the Invention
Clear, aqueous gels are prepared from certain polyoxybutylene-polyoxyethylene block copolymers. These gels are particularly useful in the formulation of topically applied cosmetic and pharmaceutical compositions because they are gels at temperatures below about 30.degree. C.
2. Description of the Prior Art
U.S. Pat. No. 3,740,421 relates to polyoxyethylene-polyoxypropylene aqueous gels. Polyoxyethylene-polyoxypropylene block copolymers form gels within certain specified ranges of compositions with water. U.S. Pat. No. 3,639,574 relates to hydrogen peroxide gels prepared employing certain polyoxyethylene polyoxypropylene block copolymers as gelling agents. U.S. Pat. No. 3,579,465 relates to polyoxyethylene-polyoxypropylene adducts of ethylene diamine which, within specified limits form aqueous gels. These gels are prepared by dissolving the block copolymer in water at a temperature between 1.degree. C. and 10.degree. C. and thereafter warming to about 30.degree. C. to form the gel.
Among the problems of these prior art gel compositions is that they liquify at temperatures below about 30.degree. C. The gels of U.S. Pat. Nos. 3,740,421, 3,639,575 and 3,579,465 are made at a temperature below at least 10.degree. C., preferably between 1.degree. C. and 7.degree. C. Therefore, they are not gels below about 30.degree. C. and cannot be stored as gels in a refrigerator or freezer. Also, the minimum quantity of the prior art block copolymers needed to make a gel is about 20 percent by weight based on the total gel weight.
It has now been found that block copolymers of polyoxybutylene-polyoxyethylene in aqueous solutions form strong ringing gels which surprisingly do not liquify below about 30.degree. C. Also, the minimum concentration of polyoxybutylene-polyoxyethylene in certain of the block copolymer gels is less than in the above-mentioned prior art gels.